The FDA is warning people not to buy these after discovering they actually contain the active prescription drug ingredients in Viagra and Cialis.

On Wednesday, the FDA issued six alerts for male sexual enhancement products that contained potentially harmful ingredients, with no mention of them on the actual product. These alerts were added to the list of many, many other sexual enhancement products that contain hidden prescription drug ingredients.

Some of the products they analyzed actually contained tadalafil, the active ingredient in Cialis. Other products contained drugs that were structurally similar to tadalafil or sildenafil, the active ingredient in Viagra. Not to mention all those "natural" ingredients on the label, which are untested, unstudied, and definitely not FDA-approved.

"It's been known for quite a number of years that male supplements have included chemicals within them that are either normally prescription medicines like generic forms of Viagra or Cialis or [are] tainted in some cases with things that don’t belong there, like heavy metals and things like that," Dr. Abraham Morgentaler, director of Men’s Health Boston, clinical professor at Harvard Medical School, tells BuzzFeed Health.

These drugs can have dangerous side effects and drug interactions, which is why they require a prescription.

For instance, taking tadalafil and sildenafil can lead to dangerously low blood pressure if you're also taking drugs containing nitrates, like nitroglycerin for heart disease or amyl nitrate ("poppers"), says Morgentaler. Plus, Viagra and Cialis do come with some rare (but possible) side effects like hearing or vision loss or an erection that won't go away.

So if you're unknowingly getting these ingredients (in unknown quantities) in your OTC sex supplement, you're putting yourself at risk for these side effects.

But, OK, what if you actually want Viagra and this gas station penis pill is calling your name?

None of the stuff on the ingredient list is actually studied or proven to work, says Morgentaler. So these products will not make your penis bigger, firmer, or last longer — unless, of course, it contains some undeclared prescription drug ingredients that shouldn't be there.

"It's understandable that they'd want to put small amounts [of prescription drugs] in these products," says Morgentaler, because if it works — even a little bit — people will keep buying it.

But if you really need erectile dysfunction medication, just get the real stuff from your doctor, says Morgentaler. The amount snuck into these supplements can't compare to the amount in an FDA-approved prescription medication.

But just so you know, not even Viagra and Cialis will give you a magic boner that lasts all night.

These drugs are approved to treat erectile dysfunction. They work by increasing blood flow to the penis, so that it's easier to get and maintain an erection. It won't turn you on, increase your stamina, or prolong ejaculation so you can go all night. And neither will these gas station penis supplements.

That's another reason you should talk to your doctor before popping a pill for your penis. They can go over other possible issues affecting your erections and tell if you if the medication will actually do what you want it to.

"We have a lot of young men asking for these medications," says Morgentaler. "Some have expectations that it's going to make their penis not only more rigid but sometimes larger, or they may be able to have sex longer. Some just have this general sense that it will make them more virile."

But that's not the case, he says, especially not for young, healthy men. "It's unlikely that if you have normal plumbing down there and you’re in your twenties that Viagra is going to give you a firmer erection."

So don't trust your erections to something with a name like Rock Hard Sex Panther XXX.